P

Hellenic J Cardiol 48: 94-107, 2007
Review Article
Pulmonary Embolism: Pathophysiology,
Diagnosis, Treatment
ELENI KOSTADIMA, EPAMINONDAS ZAKYNTHINOS
Intensive Care Unit, University Hospital of Larissa
Key words: Pulmonary
embolism risk factors,
D-dimers, computed
tomography,
anticoagulant therapy,
thrombolysis,
embolectomy.
Manuscript received:
August 9, 2006;
Accepted:
November 24, 2006.
Address:
Epaminondas
Zakynthinos
3 Tampara St.,
414 47 Larisa, Greece
e-mail:
[email protected]
P
ulmonary embolism (PE) is the third
greatest cause of mortality from cardiovascular disease, after myocardial infarction and cerebrovascular stroke.
From hospital epidemiological data it has
been calculated that the incidence of PE in
the USA is 1 per 1,000 annually.1 The real
number is likely to be larger, since the condition goes unrecognised in many patients.
Mortality due to PE has been estimated to
exceed 15% in the first three months after
diagnosis.1
PE is a dramatic and life-threatening
complication of deep venous thrombosis
(DVT). For this reason, the prevention, diagnosis and treatment of DVT is of special
importance, since symptomatic PE occurs
in 30% of those affected. If asymptomatic
episodes are also included, it is estimated
that 50-60% of DVT patients develop PE.2
DVT and PE are manifestations of the
same entity, namely thromboembolic disease.
If we extrapolate the epidemiological
data from the USA to Greece, which has a
population of about ten million, 20,000 new
cases of thromboembolic disease may be expected annually. Of these patients, PE will
occur in 10,000, of which 6,000 will have
symptoms and 900 will die during the first
trimester.
Pathophysiology of pulmonary embolism
The pathophysiology and clinical manifes-
94 ñ HJC (Hellenic Journal of Cardiology)
tations of PE depend upon four main factors: a) the extent of occlusion of the vascular tree and the size of the emboli; b) the
patient’s pre-existing cardiopulmonary condition; c) chemical vasoconstriction due to
the release of serotonin and thromboxane
from platelets that adhere to the embolus,
as well as to fibropeptide B, which is a product of fibrinogen breakdown; and d) the reflex vasoconstriction that is likely to occur
as a consequence of pulmonary artery dilatation.3,4
Effect of PE on gas exchange
Arterial CO2 pressure (PCO2) depends on
CO2 production (VCO2) in the organism
and on minute alveolar ventilation (VC),
via the equation PCO2 = k . VCO2 / VC.
The sum of VC and the minute dead space
ventilation gives the minute ventilatory gas
volume (VE).
The obstruction of flow in embolised
arteries results in the creation of dead space
in the corresponding regions of the lung
(Figure 1).5 An increase in dead space has
a direct effect on PCO2 and on end-tidal
CO 2 pressure (ETCO 2 ). If V E does not
change—as is the case in patients in the intensive care unit (ICU) under mechanical
ventilatory support and pharmaceutical
paralysis, where respiration is fully controlled—PCO2 will increase (provided that
CO2 production is unchanged). However,
most patients (with non-mechanical venti-
Pulmonary Embolism
latory support) increase VE, and indeed to a greater
extent than is required for CO2 removal (i.e. increase
VC, too), resulting in hypocapnia. Conversely, in patients with extensive PE or respiratory disorders rapid
fatigue of the respiratory muscles may ensue, with an
increase in PCO2 (hypercapnia).
In healthy individuals ETCO2 is approximately
equal to PCO2. However, after PE, since the end-tidal
air is a mixture of alveolar gas (where PCO2 is about
equal to alveolar CO2 pressure—PaCO2) and gas from
dead space (where the CO2 pressure in these alveoli is
equal to inhaled air pressure, i.e. zero), ETCO2 decreases to a degree commensurate with the extent of
the dead space (Figure 1).5
A degree of hypoxaemia, albeit small, is seen in
most patients with PE. Thus, 63% of patients have partial O2 pressure in arterial blood (PO2) <70 mmHg.
The remainder have normal PO2 as a result of hyperventilation, which may reach double or triple the normal VE. Four mechanisms have been determined to
contribute to PE hypoxaemia:6-8
a) Arteriovenous communication is created at the
levels of both lungs and heart. In the lungs it appears
that new vessels “open”, bypassing the capillaries, in an
attempt to reduce blood pressure in the pulmonary circulation. In the heart, ateriovenous communication
from right to left occurs via a patent foramen ovale—
which transoesophageal echocardiography has demon-
ET-CO2=40
strated in 60-70% of healthy individuals—when right
atrial pressure increases as a result of PE.
b) Disturbances of ventilation-perfusion (V/Q disturbances) appear to be the main mechanism of hypoxaemia. The local release of histamine causes bronchospasm, while the release of serotonin causes vasospasm, with the result that there are regions with
good perfusion and reduced ventilation (functional
shunt) and regions with good ventilation and reduced
perfusion. Furthermore, the reduced production of surfactant in the affected regions leads to their atelectasis.
c) The fall in cardiac output that accompanies a
significant degree of PE leads to a fall in O2 saturation
in mixed venous blood. This decrease in saturation exacerbates any hypoxaemia due to V/Q disturbances.
d) In extensive PE, and especially when the alveolar-arterial membrane is affected, the reduced O 2
perfusion may contribute to hypoxaemia, since an increased amount of blood is forced to pass through the
unaffected sections of the lung and thus does not
have time to be oxygenated.
Although gas disturbances are of particular interest in the pathophysiology of PE and can be of significant assistance in its diagnosis, hypoxaemia usually
responds easily to the enrichment of ventilated air
with O2. Therefore, the severity of PE arises mainly
from its effect on both the pulmonary and the systemic circulation and not on gas exchange. With few
exceptions (e.g. certain patients with chronic obstructive lung disease), the morbidity and mortality of PE
are due to cardiovascular and not respiratory failure.
ET-CO2=20
Effect of PE on pulmonary circulation
40
40
0
47
47
47
40
A
40
40
B
Figure 1. The increase in dead space and reduction in end-tidal
CO2 (ETCO2) in pulmonary embolism. In A the alveoli and their
capillaries have normal ventilation and perfusion, respectively.
ETCO2 has a normal value (40 mmHg), which is equal to arterial
CO2 (PCO2) and alveolar CO2 (PaCO2). In B we see the effect of
obstruction of the blood flow to half the alveoli. The dead space
increases, while ETCO2 is reduced to a level proportional to the
alveoli that maintain their ventilation but not their perfusion (here
one half). The minute ventilatory gas volume (VE) has been doubled in order to maintain stable PCO2 (40 mmHg).
Emboli impede the pulmonary circulation both mechanically, and through the release of hormonal substances (serotonin), as well as through other mechanisms (e.g. hypoxaemia) related to the vasospasm
they cause.7 This increase in afterload, in combination with the usual tachycardia, increases O 2 consumption by the right ventricle. The right ventricle dilates and thins, its wall stress increases, and coronary
perfusion is reduced. At the same time, cardiac output decreases, further exacerbating the hypoxaemia.
The increased O2 demand by the myocardium and the
simultaneous reduction in supply place the right ventricle at direct risk of ischaemia, which may lead to
cardiac failure (Figure 2).9 Haemodynamically, there
is an increase in right ventricular and right atrial pressure. The right atrial pressure increase may lead to
paradoxical embolism in the systemic circulation, via
(Hellenic Journal of Cardiology) HJC ñ 95
E. Kostadima, E. Zakynthinos
Figure 2. Pathophysiology of the effect of pulmonary embolism on the pulmonary and systemic circulation (modified from reference 9). IVS – interventricular septum; LV – left ventricle; PA – pulmonary artery; RV-right ventricle.
a patent foramen ovale. In addition, the increase in
pressure and volume in the right ventricle also affects
the left ventricle. The displacement of the interventricular septum from right to left changes the characteristics of the left ventricular pressure-volume curve,
worsening its distensibility and diastolic filling. The
left ventricular preload is therefore reduced, further
decreasing cardiac output (Figure 2). The sudden
pericardial tension may explain the high values of left
ventricular end-diastolic pressure and wedge pressure, while the filling pressure, which reflects preload,
is essentially reduced.10,11
If the PE is extensive enough for the mean pulmonary
pressure to exceed 40 mmHg, the right ventricle will exhibit acute failure. This is the usual cause of death in PE
patients.5 Conversely, PE of small extent is unlikely to
affect the patient haemodynamically. This can only happen in patients who already have elevated pulmonary
vascular resistances before the occurrence of embolism,
because of pre-existing cardiac or pulmonary disease.
Risk factors
The classical triad of risk factors for the occurrence of
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thromboembolic disease proposed by Virchow in
1856—local injury to the vascular wall, increased coagulability, and circulatory stasis—can explain most
cases of DVT and PE.
Prolonged immobility, advanced age, postoperative period, post-infarction period, heart failure, obesity, pregnancy, and other factors, predispose for
thromboembolic disease via venous stasis. Events
such as local trauma, vasculitis and previous thrombosis cause damage to the endothelium of the venous
wall. Polycythemia, contraceptive pills, as well as malignant cancers, and especially adenocarcinomas, are
associated with coagulability disorders and an increased risk of DVT and PE.12 A more detailed discussion follows.
Travel
The chance of massive PE during an aeroplane flight
is very small (0.4 per million passengers). It usually
involves flights of distances greater than 5000 km and
passengers over 50 years old, cancer victims, with a
history of thromboembolism, thrombophilia, or varicose veins.13
Pulmonary Embolism
Obesity
The degree of correlation between obesity and the
occurrence of PE depends on the body mass index
(BMI). The relative risk of PE has been found to be
1.7 for BMI 25-28.9 kg/m2 and 3.2 for BMI 29 kg/m2
and above.14
Contraceptives
Third generation contraceptives, which contain newer
progesterones, appear to be free of side effects such
as acne and piliation. However, they have been implicated in actions related to the coagulation mechanism, such as resistance to activated protein C; there
is thus an increased risk of thromboembolism, indeed
even greater than for second generation contraceptives.15 Advanced age and the smoking habit increase
the likelihood of complications among contraceptive
users. 16 Despite the increased risk of thromboembolism, the chance of a fatal episode of PE remains
small.17
Pregnancy
During pregnancy, the risk of thromboembolism increases with the week of gestation. It often occurs during the gestation period, but more rarely after delivery.
Advanced age and Caesarean section increase the likelihood of thromboembolic disease.18
Hormone therapy
An important meta-analysis of 12 studies determined
that the relative risk of thromboembolic disease in
women under hormone replacement therapy in the
post-menopausal period is 2.1, with higher values (3.5)
during the first year of treatment.19 An interesting randomised, placebo-controlled, prospective study found
that the risk of PE in post-menopausal women taking a
combination of oestrogen and progesterone was about
twice that in the control group.20
The incidence of PE has also been investigated
in relation to the use of raloxifen and tamoxifen for
the prevention and treatment of breast cancer. The
rate of occurrence of PE in recently published studies
was found to be 2.5 to 3 times higher than in control
groups.21,22
Cancer
The chance of diagnosing a malignancy is increased
for around 2 years after an episode of thromboembolic
disease; usually, these are cancers of advanced stage
with a consequently poor prognosis.23,24 Especially in
patients with idiopathic thromboembolic disease, the
existence of cancer is very probable and should therefore be checked for thoroughly.25
Trauma/surgery
Local trauma and orthopaedic operations, especially
in the region of the pelvis, hips, thighs and knees,
cause damage to the venous wall endothelium. It is
believed that surgery predisposes to PE, for an interval of more than a month post operation. It has been
found that 25% of cases of PE occur 15-30 days after
surgery, and 15% after the 30th day. The 18th postoperative day has the highest degree of risk.26
Thrombophilia
In one fifth of cases, genetic predisposition is the main
cause of PE, although one of the classical risk factors
from Virchow’s triad may also be present. The doctor
should suspect genetic predisposition when there is:
a) a strong family history of thromboembolic disease;
b) thrombosis in unusual anatomical sites (upper body
or upper limbs, when there is no central line catheter);
c) repeated thrombosis with no known risk factors; d)
thrombosis occurring at a young age; e) resistance to
usual anticoagulant therapy.
It has been known for a long time that a lack of
protein C, protein S, and antithrombin III is associated with an extremely high risk of thromboembolic disease. However, these genetic abnormalities are only
identified in 5% of patients with DVT.27 In an even
smaller percentage of these patients, insufficiency of
the fibrinolytic system (hypoplasminogenaemia, abnormal plasminogen, insufficiency of plasminogentPA activator) and insufficiency of factor XII may be
encountered. Relatively recently, a mutation of factor
V has been found (replacement of arginin with glutamin in position 506 on factor V) which is known as
factor V Leiden. This hereditary abnormality is encountered in a high proportion of the general population with heterozygous dominant form (3-4%) and is
responsible for 20% of cases of DVT.27 Factor V Leiden increases coagulability, causing resistance to activated protein C.28,29 Even though by itself factor V
Leiden exerts only a mild thrombogenic effect, increasing coagulability by 2-3 times, the knowledge of
its existence is extremely important in circumstances
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E. Kostadima, E. Zakynthinos
that increase resistance to activated protein C, such
as the use of contraceptive tablets or pregnancy. The
use of contraceptives in combination with factor V
Leiden increases the likelihood of thromboembolic
disease by 35 times.30 In conditions of increased probability of thromboembolic disease—prolonged immobility, postoperative period, etc.—it is essential to
intensify preventive treatment in patients who are
carriers of this factor.31,32
An elevated titre of antiphospholipid antibodies,
especially lupus anticoagulant, is found in around 8.5%
of cases of DVT, while being practically nonexistent
in the general population.33 It should be noted that a
large number of patients with positive lupus anticoagulant do not suffer from systemic lupus erythematosus.
Hyperhomocysteinaemia is usually an acquired
abnormality, which increases the risk of thromboembolic disease by 2-3 times and is due to an insufficient
intake of vitamins B1 and B6.34
The investigation of hypercoagulant states in the
acute phase of thromboembolic disease must necessarily include checks for: a) Factor V Leiden, because
it is the most common anomaly responsible—checked
using polymerase chain reaction; b) Hyperhomocysteinaemia, because it may usually be treated completely and quickly by the administration of vitamins
B1 and B6; c) Lupus anticoagulant, because if it is present it requires intensive and immediate therapy. In
the acute phase it is not necessary to check protein
C, protein S, or antithrombin III, firstly because they
are rarely deficient, and secondly because their levels
in the blood decrease in acute thrombosis. In addition, heparin lowers antithrombin III levels, while
coumarin anticoagulants reduce the levels of proteins C and S.
Diagnosis
The clinical diagnosis of PE is particularly difficult,
since it may easily be confused with other conditions; as
a result it is often overlooked (Table 1). Venous thromboembolic disease is often asymptomatic, which adds
to the difficulty, while when symptoms of PE are present they tend to be non-specific. Tachycardia, chest
pain, cough, unexplained loss of consciousness,
and/or haemoptysis, raise the suspicion of PE, while
hypoxaemia, haemodynamic instability, syncopal
episode and/or cyanosis are characteristic of massive
PE.36-38
Large series of patients have been studied with a
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Table 1. Differential diagnosis of pulmonary embolism.
Pneumonia or bronchitis
Asthma
Exacerbation of chronic obstructive pulmonary disease
Myocardial infarction
Pulmonary oedema
Anxiety-hysteria
Aortic dissection
Lung cancer
Primary pulmonary hypertension
Rib fractures
Pneumothorax
Musculoskeletal pain
view to evaluating the role of clinical signs, findings
and symptoms in the diagnosis of PE (Table 2).36,39
Pain of pleuritic type is usually associated with
peripheral embolism, which causes irritation of the
pleura and is associated with pulmonary infiltration
on X-ray. Histopathologically, it is associated with
alveolar haemorrhage, often with haemoptysis as a
symptom.39,40
Dyspnoea is mainly associated with central PE,
which does not affect the pleura, although the haemodynamic consequences are more serious. It is the most
common symptom, while tachypnoea (>20 breaths/
minute) is the most frequent sign of acute PE (7080% of patients with angiographically proven PE exhibit dyspnoea).36
On clinical examination tachycardia is usually
seen, while there may be signs of right heart failure,
such as dilation of the jugulars with a V wave, left
parasternal cardiac pulsion, greatly increased pulmonary element of the second heart sound, and a systolic murmur, low left parasternally, increasing during
inspiration on auscultation, probably with a third
sound in the same region. These symptoms, of course,
are often masked by tachypnoea, obesity, pithoid
chest, etc.35
In arterial blood gases, the coexistence of hypoxaemia and hypocapnia help in the diagnosis of PE.
However, these signs are not specific, since PO2 and
PCO2 may be normal, especially in young people with
no prior disease. In addition, PCO2 may be elevated
in patients with massive PE. ETCO 2 is always reduced, but lacks specificity.4-6,38
The presence or absence of risk factors for venous thromboembolic disease is an essential piece of
knowledge for the evaluation of the likelihood of PE.
We should be aware that the risk of PE increases with
the number of risk factors present, and that PE does
Pulmonary Embolism
Table 2. Symptoms, clinical signs, and common laboratory findings
in suspected pulmonary embolism (PE) in the intensive care unit.37,40
PE
No PE
(n=219) (n=546)
Symptoms:
Dyspnoea
Pleuritic pain
Retrosternal pain
Cough
Haemoptysis
Syncopal episode
80%
52%
12%
20%
11%
19%
59%
3%
8%
25%
7%
11%
Clinical signs:
Tachypnoea (>20/min)
Tachycardia (>100/min)
Signs of DVT
Fever (>38.5oC)
Cyanosis
70%
26%
15%
7%
11%
68%
23%
10%
17%
9%
Radiological findings:
Atelectasis
Pleuritic effusion
Peripheral opacification (infarct)
Raised hemidiaphragm
Reduced pulmonary vascularisation
49%
46%
23%
36%
36%
45%
33%
10%
25%
6%
Blood gases:
Hypoxaemia
75%
81%
Electrocardiogram:
Right ventricular hypertrophy
50%
12%
DVT – deep venous thrombosis
not usually occur in the absence of any risk factors.41
Isolated clinical signs and symptoms are not useful,
since they have neither good sensitivity nor satisfactory specificity (Table 2). For this reason, Wells et al42
proposed a prognostic rule (pretest probability) incorporating 7 weighted variables for the diagnosis
of PE: existence of clinical signs and symptoms of
thromboembolic disease (3 points), absence of alternative diagnosis (3 points), heart rate above 100 (1.5
points), immobility or surgery during the previous 4
weeks (1.5 points), previous thromboembolic disease
or PE, (1.5 points), haemoptysis (1 point), and malignancy (1 point). A total score less than 2 means low
probability, 2-6 points medium probability, while a
score of over 6 points suggests a high probability of
PE.
Although the electrocardiogram and chest X-ray
are of limited value, often being normal in patients
with PE, they should nevertheless be taken into account.35 The most common electrocardiographic find-
ings are tachycardia and T-wave inversion in the precordial leads.43 A right axis deviation of the form SπQπππ-Tπππ, first appearance of incomplete or complete
right bundle branch block, as well as pulmonary Pwaves or atrial fibrillation occur more rarely (<12%
for each).44
The chest X-ray is mainly of help in ruling out other conditions (e.g. pneumothorax, pulmonary oedema,
pneumonia) that have clear radiological findings, and
is of less use in the diagnosis of PE. The radiological
signs of PE are non-specific (mild pleural effusion,
raised diaphragm, atelectasis), or especially difficult to
evaluate (protruding pulmonary artery—Knuckle sign,
diaphragm-based truncated cone—Hampton’s hump
sign, local oligaemia—Westermark sign, dilatation of
the right superior pulmonary artery—Palla sign). In
25% of cases of PE the chest X-ray is normal. In fact,
this is of great assistance, because the coexistence of
severe dyspnoea, with a ventilation-perfusion lung
scan of even intermediate probability, is practically diagnostic for PE.4,8,45
The white cell count is usually normal or slightly
elevated and is not of help in diagnosis. Also, the classical triad of increased lactate dehydrogenase (LDH),
increased bilirubin, in combination with normal levels
of transaminases, is seen in only 4% of cases, while
the combination of high LDH levels with normal
SGOT is found in only 20%. Goldhaber et al46 found
bilirubin >2.0 mg/dl and LDH >400 M/L each in
20% of cases. The only haematological examination
that helps in the diagnosis of PE is the measurement
of D-dimers with the ELISA method. Although this
method is very sensitive (>90%) it is non-specific,
since elevated levels of D-dimers are found in many
disease conditions that are clinically similar to PE,
such as myocardial infarction, pneumonia, heart failure, cancer, post-surgery, trauma, etc. In view of this,
the most important contribution of D-dimers is in ruling out PE when their levels are normal (high negative predictive value).47,48
The role of cardiac biological indexes as prognostic indexes of PE has already attracted great interest.
Elevated troponin levels are associated with high mortality,49 as are high levels of pro-brain natriuretic peptide (pro-BNP), in contrast to low concentrations of
pro-BNP, which as a rule are associated with a good
clinical outcome.50-52
Perfusion lung scanning is a basic non-invasive
examination for the diagnosis of PE. It is based on the
embolisation of colloidal radioactive tracer particles
in regions of the lung that maintain their perfusion.
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E. Kostadima, E. Zakynthinos
Thus, the normal regions opacify, while the regions
that have undergone PE do not.46,53 Despite initial
enthusiasm, this examination has not managed to replace angiography, since its specificity is not satisfactory in the diagnosis of PE. Every cause of reduced
perfusion in a region of the lung, such as hypoxic vasospasm, or the presence of a West I zone, causes a
perfusion defect indistinguishable from those of PE.
False positive perfusion scans are seen in patients suffering from asthma, chronic obstructive pulmonary
disease, atelectasis, pneumonia, hypovolemia, etc., as
well as in patients who are on mechanical ventilation
with positive end-expiratory pressure.3 In contrast to
the pathological scan (which is non-specific), a normal scan is particularly useful, essentially ruling out
PE, since perfusion scintigraphy has high sensitivity.46
The specificity of the perfusion scan increases when it
can be combined with a ventilation scan. The pulmonary embolus shows a perfusion defect that is not
associated with a ventilation defect, or if one exists,
the ventilation defect is small. Conversely, a perfusion
defect that is due to hypoxic vasospasm is usually of
smaller size than the corresponding ventilation defect.4,46,53
For ease of evaluation, ventilation-perfusion (V/Q)
scanning is classified as high probability, intermediate
probability and normal. In order to be classified as
high probability for PE, a V/Q scan must have two or
more pulmonary regional perfusion defects, with no
or very small changes in the ventilation scan and on
the chest X-ray. A high probability V/Q scan has 85%
specificity in the diagnosis of PE, while for the intermediate probability scan the specificity is low. Unfortunately, however, high probability scans have low
sensitivity. In the PIOPED study it was found that only 41% of patients with angiographically proven PE
had a high probability V/Q scan.53 This means that
most patients with PE have an intermediate probability or a normal scan. Thus, the V/Q scan is considered
particularly useful: a) when it is found to be normal,
almost ruling out PE (especially when combined with
negative D-dimers), and b) when it is classified as
high probability, in which case full treatment is recommended, without the need for angiography. Of
course, the presence of another positive examination,
or a high clinical suspicion of PE, reinforce the diagnostic conclusion. In the case of an intermediate
probability scan further investigation is considered essential.54
Spiral computed tomography (CT) of the lung,
with intravenous infusion of radiopaque medium, has
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been widely used in recent years for the diagnosis of
PE. Until recently, it had good sensitivity and specificity in the identification of emboli in the large pulmonary arteries (80% and 90%, respectively), but it
was less successful in the peripheral vascular tree—
beyond the third level of branching in the pulmonary
circulation.55 The new, multi-slice tomographic devices seem to be a great improvement in this respect.
In a recent multi-centre study that used multi-slice
CT, the sensitivity and specificity were substantially
better (83% and 96%, respectively). Furthermore, if
CT was combined with imaging of the venous phase,
the sensitivity increased significantly (90%) with no
reduction in specificity. The positive prognostic value
was evaluated as >90% if there was clinical suspicion
of PE (96% with high clinical suspicion, 92% with intermediate clinical suspicion). 56 A combination of
multi-slice CT and negative D-dimers essentially ruled
out PE.57
Magnetic resonance pulmonary angiography with
gadolinium may prove to be particularly safe and useful in the future,58 since apart from anatomical characteristics it provides information about right ventricular wall motion.59
Transthoracic echocardiography is considered
useful in the diagnosis of pressure overload in the
right chambers. Thus, it is of particular use in identifying patients with a large PE, in whom the pressure
of the pulmonary circulation is elevated (90% sensitivity). 60 In these patients we can see dilatation of
the right ventricle and hypokinesis of its free wall,
while at the same time the shape of the left ventricle
changes, because of the displacement and flattening
of the interventricular septum, adopting a D shape
on its short axis during both systole and diastole.61 A
characteristic sign is the maintenance of mobility of
the apical region of the right ventricle—McConnell
sign62—in contrast to the hypokinesis of the entire
free wall that is observed in chronic pulmonary hypertension. 63 Measurement of systolic pulmonary
pressure is feasible in 80-90% of cases with significant PE, via the accompanying tricuspid regurgitation, while diastolic pressure may be measured if
there is also pulmonary valve insufficiency (Doppler
measurements).63 However, in a recently published
prospective study64 the echocardiogram was normal
and failed to confirm the diagnosis in 50% of patients with angiographically determined PE. The
transoesophageal echocardiogram, a bedside examination, is considered especially useful in ICU patients with haemodynamic instability where moving
Pulmonary Embolism
them away from the unit in order to perform CT, MRI,
etc., is difficult. Apart from the aforementioned
findings, transoesophageal echocardiography can reveal the existence of thrombus in the main trunk or
the pulmonary arteries in 80% of cases with massive
PE (Figure 3).65,66
Pulmonary angiography continues to be the gold
standard in the diagnosis of PE, and should be performed when other examinations have failed to solve
the problem. If the patient’s condition permits, it
should be performed during the first week after the
start of episodes of PE, since after this period spontaneous revascularisation has been observed in a large
number of cases. Angiography is quite a safe examination, with mortality as low as 0.2%.67 Mortality increases in patients who have a severe degree of pulmonary hypertension (systolic pulmonary pressure
>70 mmHg and right ventricular end-diastolic pressure >20 mmHg), but even in such cases it does not
exceed 2%.68
Lower limb ultrasound, provided it includes compression ultrasonography, is the examination of choice
in patients with symptoms of DVT,69 having a sensitivity and specificity of 73% and 90-100%, respectively.70,71 Both impedance plethysmography and phlebography (despite still being considered a gold standard) are beginning to become marginalised.72 Ultrasonography is precise when it is performed in symptomatic patients with a suspicion of DVT, but its sensitivity is much lower when there are no signs of phlebothrombosis.73 This seems to be because its sensitivity is high in the evaluation of thigh veins, but not in
the smaller, branching veins of the shins and the noncompressible veins of the pelvis.74,75 In these cases
magnetic resonance angiography has given good results, while promising even more in the future.76
For the successful evaluation of patients in whom
PE is suspected, clinical signs and symptoms should
be combined with diagnostic laboratory examinations.
Thus, for example, patients with a high probability
V/Q scan or a positive spiral CT should be treated for
PE. For patients with a pathological V/Q scan—not
high probability—even with a negative spiral CT examination, there is the likelihood of PE. In such cases
compression ultrasonography should be performed. If
it is positive, treatment ensues, while if the results are
negative the chance of disease is extremely limited.
Clinical studies have determined that in suspected PE
the combination of negative spiral CT with negative
compression ultrasonography safely rules out the disease.77-79 For patients with a non-high probability V/Q
scan and negative spiral CT the disease may be ruled
out when the pretest probability42 is low, or D-dimers
are negative. In the remaining patients angiography
should be performed, or they should be followed for at
least one week with compression ultrasonography, especially if the pretest probability is high. Apart from directing the choice of the most appropriate examination
at each stage of diagnosis, diagnostic algorithms can also help to rule out PE early, thus avoiding unnecessary
laboratory examinations. Various algorithms have
been proposed, depending mainly on the diagnostic
methods available and the experience in each centre.
In figure 4 a diagnostic algorithm is proposed that
could be adopted by most centres.
Treatment
The cornerstone of therapy for PE is the prevention
of new embolic episodes with anticoagulant treatment
or a filter in the inferior vena cava, since it has been
found that the majority of patients do not die from
the embolism that leads to diagnosis, but to the continuing deterioration of their condition due to new
emboli.80-82 However, when the patient is in shock, or
the haemodynamic condition is particularly poor, it is
necessary to attempt primary lysis of the thrombus/
embolus using thrombolysis or some invasive embolectomy technique.
Figure 3. Transoesophageal echocardiogram, showing a large
thrombus in the right main pulmonary artery (RPA) that confirms
the diagnosis of massive pulmonary embolism. (From reference
66, reproduced with permission.)
Supportive therapy
The patients often present with hypoxaemia, which
(Hellenic Journal of Cardiology) HJC ñ 101
E. Kostadima, E. Zakynthinos
Figure 4. Diagnostic algorithm when there is suspicion of pulmonary embolism (PE).
*Alternatively, according to the capabilities of the diagnostic centre, spiral computed tomography (CT) could be performed, or repeated
compression ultrasonography (CUS) of the lower limbs, on the 1st, 3rd, 7th and 14th day.
responds to O2 administration, since the main pathophysiological mechanism is V/Q disturbances. Bed
rest appears to help via two mechanisms. First, the restriction of movement reduces the likelihood of thrombus detachment from its peripheral location; second,
it reduces O2 consumption (VO2) and therefore the
need for increased cardiac output. In extreme cases
of patients in shock, it may be necessary to instigate
pharmaceutical muscle paralysis and mechanical ven102 ñ HJC (Hellenic Journal of Cardiology)
tilation in the ICU, in order to reduce VO2 to the minimum.10
Noradrenaline may be used in severe cases, since
by inducing peripheral vasospasm it can increase the
pressure in the aorta and the flow to the coronary vessels (improving right heart ischaemia), without affecting right ventricular afterload.83 Other inotropic drugs
(dopamine, dobutamine, isoproterenol and adrenaline) appear to have no place in PE, since they increase
Pulmonary Embolism
O2 consumption without a corresponding improvement in cardiac output.10
Fluid administration is contraindicated, as further
dilatation of the right ventricle leads to an increase in
myocardial O2 consumption and greater restriction of
the left ventricle, because of the displacement of the
interventricular septum, and therefore a reduction in
cardiac output.84
Relatively recently, low molecular weight heparin
has been used in the treatment of haemodynamically
stable PE, with similar efficacy and greater safety
compared to standard heparin.81,94,95 It should be noted, though, that treatment with low molecular weight
heparin has not been used for massive PE and should
not be used until the necessary studies have been reported.
Anticoagulant therapy
Filter placement in the inferior vena cava
Heparin is the basic treatment for PE, preventing the
formation of new thrombi and giving time for the endogenous fibrinolysis to take effect, dissolving older
thrombi.80,85 Heparin administration should be started
immediately, even before the diagnosis of PE is established, provided that anticoagulant therapy is not contraindicated. The recommended regimen is rapid intravenous administration of 5,000-10,000 IU (80
IU/kg), followed by a continuous drip infusion of
1,000-1,200 IU (18 IU/kg) per hour. The maintenance
dose is determined by the activated partial thromboplastin time (aPTT), which should be between 60 and
80 s (aPTT=1.5-2.5 times that before heparin administration). If the aPTT is below the lower limit desired,
the maintenance dose is increased by 200 IU, and a
rapid bolus infusion is given (for aPTT <35 s, 80 IU/
kg; for aPTT 35-40 s, 40 IU/kg).86,87 In patients who
are resistant to heparin—defined as inability to achieve the desired aPTT with drip infusion above 50,000
IU/24 hours—and in patients who exhibit thromboembolic disease with high aPTT prior to heparin administration (patients with lupus anticoagulant or other antibodies against anticardiolipin), the dosage is determined on the basis of serum heparin levels (0.3-0.4
IU/ml).88 Once the desired aPTT has been achieved,
oral coumarin anticoagulants may be given. Coadministration with heparin is required for 5 days, since the
full anticoagulant effect of coumarins is achieved within that time.89 The desired international normalised
ratio (INR) in this case is 3, as heparin administration
prolongs it somewhat. An INR of around 2.5 is ideal
after heparin is discontinued. The duration of anticoagulant therapy after PE has not yet been firmly established. The minimum interval seems to be 6
months.90 In patients with repeated episodes of PE,
lifelong treatment may be required, 91 while in patients deficient in antithrombin III, protein C or S,
and those with factor V Leiden and PE, therapy is
likely to be needed for many years, but not for the
rest of their lives.92,93
Filter use is indicated in cases of PE where there are
contraindications for anticoagulant administration
(active haemorrhage, endangered haemorrhage following severe brain injury or craniotomy), or when repeated episodes of PE occur despite full anticoagulant therapy.85 Filters do not appear to help in cases
of proximal DVT with free-floating thrombus,96 while
their combination with anticoagulants does not improve survival in comparison with anticoagulant therapy alone.97
Thrombolysis
Thrombolysis should be performed immediately in
patients with circulatory shock, or obvious haemodynamic instability (massive PE). The outcome in these
patients is clearly better in comparison with anticoagulant therapy alone.98-101 A recent meta-analysis found a
significant reduction in deaths and PE reoccurrence
in studies that included haemodynamically unstable
patients (9.4% versus 19%).98
In patients with stable blood pressure, but signs of
right cardiac dysfunction on echocardiography (submassive PE), there is no consensus regarding the use of
thrombolysis.102-110 Konstantinides et al,108 in a recent
large, randomised, blind study in which heparin was administered with either alteplase or placebo, observed a
better clinical course in the patients who were given alteplase. Specifically, they found that in the alteplase
group (rt-PA) fewer patients needed scaling of therapy, i.e. a need for inotrope administration, secondary
thrombolysis because of circulatory shock, intubation
and mechanical ventilation, emergency surgical embolectomy, or cardiopulmonary resuscitation (24.6%
versus 10.2%, p=0.004). However, the mortality did
not differ between the two groups.108
Supporters of thrombolysis in patients with submassive PE maintain that it directly improves cardiac
function, while at the same time reducing the episodes of reembolisation in these patients. 104,108-110
(Hellenic Journal of Cardiology) HJC ñ 103
E. Kostadima, E. Zakynthinos
Those who argue for heparin treatment alone in patients with submassive PE, base their position on the
increased risk of haemorrhage as a result of thrombolysis. 105,106 The recent meta-analysis mentioned
above98 found that thrombolysis was associated with a
non-significant increase in major haemorrhages (9.1%
versus 6.1%; OR 1.42, 95% CI 0.81-2.46) but with a
significant increase in minor haemorrhages (22.7%
versus 10.0%; OR 2.63, 95% CI 1.53-4.54).
From the above it appears that the benefit of thrombolysis in this group of patients with submassive PE
should be assessed together with the risk of major
haemorrhage, which increases with age.105,106 Reviewing a recent disagreement in the literature between
Konstantinides109 and Dallen,106 concerning the role
of thrombolysis in submassive PE, Goldhaber107 concluded that thrombolysis would most probably have a
place in the subgroup of patients who are haemodynamically stable but at high risk. High risk patients
could be defined on the basis of echocardiographic
criteria and cardiac biological indexes (troponin, brain
natriuretic peptide). This would, of course, need to be
evaluated in a randomised, prospective study.
In the case of thrombolysis, rt-PA in a dosage of
100 mg, in continuous drip administration within two
hours, seems to be superior to urokinase and streptokinase, which are also used. Thrombolysis is effective (administration window) even 14 days after PE.111
Newer thrombolytic drugs that are used in cases of
infarction (reteplase, tenecteplase, lanoteplase) have
not been tested in randomised studies of PE and
should not be given. For patients in whom aggressive
intervention is necessary, but the risk of haemorrhage is high, the decision for embolectomy is considered mandatory.112,113
Embolectomy
In patients with haemodynamic instability, in whom
thrombolysis has failed or is contraindicated (intracranial haemorrhage, recent surgery or trauma), transvenous catheter thrombectomy is performed.112 Various
devices have been developed for the aspiration or pulverisation of thrombus in the pulmonary circulation.114
If such a device is not available, or the procedure fails,
surgical thrombus removal is indicated, with open thoracotomy and extracorporeal circulation.115,116 Although
emergency embolectomy has found wide acceptance,
the results are not satisfactory, since the condition of patients who are referred for surgery is extremely serious.
Meyer et al112 reported 58% mortality among patients
104 ñ HJC (Hellenic Journal of Cardiology)
undergoing emergency embolectomy who suffered cardiac arrest. Cardiac arrest and cardiogenic shock are independent additional risk factors.117,118 Rapid diagnosis
and haemodynamic stabilisation play a determining role
in the improvement of results.117,118
Pulmonary endarterectomy in patients with pulmonary hypertension and evidence of thromboembolic disease on pulmonary angiography has been welldocumented in the literature.119-123 Although the incidence of the disease after an acute episode of PE is
hard to determine—many cases remain undiagnosed—
it is estimated to be around 3.8% during the two first
years after PE.124 These patients, if left without surgical
treatment, have an extremely poor prognosis. The results from centres with experience in these procedures
are of great interest. They report a significant reduction in mean pulmonary pressure and pulmonary resistances, and mainly a significant improvement in the patients’ World Health Organisation functional class,
with high 5-year survival (74-86%).122,123 The perioperative mortality depends entirely on the experience of
the centre. It seems that with greater experience mortality is limited to 4.4-9%.121-123 Independent factors
affecting in-hospital mortality are advanced age (>60
years) and the existence of mainly peripheral, and not
central, thrombi in the pulmonary circulation.123 Persistent pulmonary hypertension and haemorrhage are
the usual causes of perioperative death.122,123
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(Hellenic Journal of Cardiology) HJC ñ 107